refs and cleanup

Author: SimonCropp

src/Directory.Packages.props

@@ -5,8 +5,8 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.0.0" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
-    <PackageVersion Include="Polyfill" Version="9.11.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageVersion Include="Polyfill" Version="9.13.0" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.172" />
     <PackageVersion Include="TestableIO.System.IO.Abstractions" Version="22.1.0" />
     <PackageVersion Include="TestableIO.System.IO.Abstractions.Wrappers" Version="22.1.0" />